Thanks everyone. This was helpful. Last night, I left it face up on the nightstand, instead of putting it on the winder, and it gained around two seconds, rather than losing two. Since being early is always better than being late, a couple of seconds fast bothers me not at all.
I have an Omega Speedmaster 38 (caliber 3330), which wobbles like there’s a tiny hamster on a wheel inside, and other quirks, but it never seems to drift more than a second fast, regardless. My Hamilton Khaki 38 auto gains 2 seconds consistently. I’d assumed this Aqua Terra would behave the same, if not more consistently. And I didn’t understand how the -0/+5 was calculated (thanks for that!).
Oddly enough, this reminds me of my Seiko 5 watches (snkl23 and snk809, because the internet), which gain and lose consistently throughout the day, but do both so consistently that they average out to never being too far out of time.
Anyway, you all helped talk me down off the ceiling, for which I am grateful.